Residual Stress Sensitivity of Case-Hardened Notched Specimen

Author:  Krug, Lang, L
Source:  Conf Proc: ICSP-9 (pg 235-240)
Doc ID:  2005091
Year of Publication:  2005
ABSTRACT Case-hardened gear wheels e.g. in vehicle transmissions are very high cyclically stressed components. Their lifetime is determined by the interaction of loading, tooth flank load-capacity and tooth foot load-capacity. The latter is influenced by a multitude of parameters. One of them is the residual stress state which appears during operation. In this contribution results from the investigation of case-hardened notched specimen with different residual stress states under a cyclic bending loading without and with mean loading are reported. The load capacity of the specimens are analysed using a local concept and an additional consideration of a fracture mechanical approach. The different residual stress states arose from the case-hardening treatment on the one hand and were produced by different shot peening treatments on the other hand. The different specimen variants exhibit strongly different fatigue strengths and different dependencies of the fatigue strength on the mean loading. With the local concept it was possible to determine the crack initiation site which was partly at the surface and partly below the surface. The fracture mechanical approach was necessary to understand the crack stop behaviour e.g. of surface cracks which develop especially at shot peened specimens. Using a local concept a uniform description of all notched specimen variants could be achieved by a modified Haigh diagram which takes into account the local stress condition at the failure critical site.

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